Heating arrangement for dry copying machines

ABSTRACT

This invention provides an improved heating arrangement for the semi-cylindrical cowl of a dry copying machine, with an automatic cut-out switch operated by thermal expansion of the cowl. The cowl heater is in an external longitudinal rib on the cowl and the switch is operated by a longitudinally extending reaction rod of low expansion coefficient attached at one end to the cowl, the switch itself being carried at one end of a longitudinal bar of high expansion coefficient attached at its opposite end by one or more strips of low expansion coefficient to the end of the cowl adjacent the reaction rod. The thermal expansion of the bar and strips compensates for that of the rod during the warm-up period of the machine, allowing the latter to reach its operating temperature rapidly.

United States Patent [191 Di Muriaglio [5 HEATING ARRANGEMENT FOR DRY COPYING MACHINES [75] Inventor: Cesare Marchettl San Martino Di Muriagllo, Turin, Italy [73] Assignee: C.R.T. Italla S.r.l., Turin, Italy [22] Filed: Aug. 1, 1973 [21] Appl. No.: 384,537

[30] Foreign Application Priority Data Aug. 22, 1972 Italy 69686/72 [52] US. Cl 219/216, 219/388, 219/512 [51] Int. Cl. H05!) l/02 [58] Field of Search 219/216, 243, 244, 388,

[56] References Cited UNITED STATES PATENTS 3,243,579 3/1966 Sussin 219/216 X 2,162,589 6/1939 Rich 219/243 X 2,799,949 7/1957 Richman 219/243 X Mar. 19, 1974 3,234,868 2/1966 Appeldorn et a1 219/216 X Primary Examiner-C. L. Albritton Attorney, Agent, or Firm-Sughrue, Rothwell, Mion, Zinn & Macpeak [57] ABSTRACT This invention provides an improved heating arrangement for the semi-cylindrical cowl of a dry copying machine, with an automatic cut-out switch operated by thermal expansion of the cowl. The cowl heater is in an external longitudinal rib on the cowl and the switch is operated by a longitudinally extending reaction rod of low expansion coefficient attached at one end to the cowl, the switch itself being carried at one end of a longitudinal bar of high expansion coefficient attached at its opposite end by one or more strips of low expansion coefficient to the end of the cowl adjacentthe reaction rod. The thermal expansion of the bar and strips compensatesfor that of the rod during the warm-up period of the machine, allowing the latter to reach its operating temperature rapidly.

2 Claims, 4 Drawing Figures SHEET 2 [1F 2 PATENTEU MR 1 9 I974 The present invention relates to heating arrangements for dry copying machines of the type in which sheet material is caused to pass through a gap between a rotating cylinder and a substantially semicylindrical heating cowl of material having a high coefficient of thermal expansion, the said cowl being provided with electrical heating means controlled by a switch having a movable operating element which is actuated by thermal expansion of the cowl and which is connected at one end to a reaction rod of a material having low coefficient of thermal expansion extending parallel to the longitudinal axis of the cowl and fixed at the other end to the cowl. Such a heating arrangement is referred to herein as a heating arrangement of the type described.

An object of the present invention is to provide an improved heating arrangement for a dry copying machine of the abovementioned type for the purpose of enabling the heating cow] to attain its operating temperature rapidly during varying conditions of operation of the machine, such temperature being defined within very restricted limits of tolerance.

According to the present invention there is provided a heating arrangement of the type described, characterised in that:

a. the cowl is provided in the central part of its external surface with a longitudinally extending rib containing the electrical heating means and with two longitudinal flanges extending along the lateral sides of the rib and defining together with the outer surface of the rib a longitudinal channel;

b. the reaction rod is connected at one end to a support carried by the two longitudinal flanges of the cowl at one end thereof and acts, at its opposite end, on a lever which co-operates with the movable operating element of the switch, the said lever being pivotally mounted between the longitudinal flanges at the end of the latter opposite that to which the reaction rod is connected; 1 c. at least one strip of material having a lower coefficient of thermal expansion than that of thecowl is attached to and extends longitudinally beyond the flanges adjacent the end of the cowl to which the reaction rod is'fixed, the or each strip supporting one end of a bar having high coefficient of thermal expansion extending within the said channel and supporting, at its opposite end, the said switch.

The invention will; now be described, by way of nonlimiting example, with reference to the accompanying drawings, in which:

FIG. '1 is a plan view of a heating arrangement for dry copying machines according to one embodiment of the present invention;

FIG. 2 is a section taken on line II II of FIG. 1;

FIG. 3 is a side elevation partly in section of the arrangement shown in FIG. 1, and

fig. 4 is a perspective view of part of the arrangement illustrated in FIGS. 1- to 3, sectioned on the line IV IV of FIG. 3.

Referring to the drawings, reference 1 indicates a semi-cylindrical heating cowl of a dry copying machine. The cowl l is utilised to heat material in sheet form which is caused to pass through the gap between the internal surface of the cowl and the surface of a rotating cylinder.

The cowl 1 is constructed of material having a high coefficient of thermal expansion, such as, for example, aluminium, and is provided in the central part of its external surface with a longitudinally-extending rib 2 incorporating electrical heating means constituted by two resistances 3, 4 extending longitudinally inside an elongate block 5 of insulating material within the rib 2.

Two longitudinal flanges 6, 7 extend along the two sides of the central rib 2, parallel to the central plane of symmetry of the cowl 1. The two flanges 6, 7 and the upper surface of the rib 2 (as seen in FIG. 4) define a channel which extends longitudinally over the entire length of the cowl l.

A rod 8 consisting of material of low coefficient of thermal expansion such as, for example, invar, extends longitudinally above the channel between the flanges 6, 7. The rod 8 is provided with a threaded end 8a screwed into the central part of a U-shaped stirrup 9 located between the flanges 6, 7 at one end of the cowl l and secured to the flanges, for example by rivets.

The opposite end of the rod 8 has an enlarged head 8b which bears against a transverse wall of a lever 10 of U-section articulated to a transverse pivot pin 11 supported between the two flanges 6, 7. The lever 10 carries a feeler 12 adapted to co-operate with the operating element of a switch 13 connected in the electrical supply circuit of the heating resistances 3, 4.

The switch 13 is fixed to a support block 14 having an axially extending aperture 15 therein through which the rod 8 passes. The support block 14 has a lower appendage 14a of U-section into which fits one end of a square-section bar 17, the bar 17 being fixed to the appendage 14a by means of a screw 16.

The bar 17 is of a material having high coefficient of thermal expansion such as, for example, aluminium, and extends longitudinally in the channel comprised between the flanges 6 and 7, the bar 17 projecting a certain distance beyond the opposite end of the cowl 1 from the support block 14. The outer projecting end of the bar 17 is connected by means of a transverse bolt 18 to two strips 19 and 20 of iron or other material of lower coefi'icient of thermal expansion. The strips 19, 20 extend, as shown inFIGS. 1 and 3, over acerta'in distance along the lateral surfaces of the flanges 6, 7 and these respective flanges are fixed by means of screws 21.

The bar 17 therefore overhangs from the outer ends of the two strips 19, 20, the portion of the bar 17 extending longitudinally in the channel between the flanges 6, 7 and rib 2 being spaced from the inner surface of said channel.

When the switch connecting the electrical supply to the heating resistances 3, 4, is closed, heat is immediately transmitted through the rib 2 which surrounds such resistances to the flanges 6, 7. Since the coefficient of expansion of the flanges 6, 7, is much greater than that of the rod 8, the latter functions as reaction rod through the head 8b which bears against the lever 10 causing the latter to pivot in the direction indicated by the arrow F, to bring the feeler 12 into engagement with the switch 13 and open the latter.

Because the switch 13 is secured to the free'end of the bar 17 which is connected at its other end of the flanges 6, 7 through the strips 19, 20 as described above, the following favourable effects are afforded in operation. a Initial Heating Assuming all parts of the device are at room temperature when the switch 13 is closed, the flanges 6, 7 are quickly heated by the resistors 3, 4 and transmit heat to the strips 19, 20 which expand and move the bar 17 axially to the right as seen in FIGS. 1 and 3. At this initial heating stage the bar 17, which is thermally insulated from the flanges 6, 7 and rib 2 by the provision of the air gap between the external bar surface and inner surface of the abovementioned channel expands by a negligible extent as compared with the strips 19, 20.

Consequently, the switch 13 is moved to the right in FIGS. 2 and 3 away from the feeler 12 on the lever 20.

This delays breaking of the electric circuit feeding current to the resistors 3, 4 whereby the cowl 1 reaches quickly its predetermined temperature.

b. Prolonged Operation When the device is operated at length the heated Invar rod 8 would tend by expanding to rotate the lever 10 in a counter clockwise direction, that is, opposite the arrow F (FIG. 3), thereby gradually increasing the gap between the feeler l2 and switch 13. This would lead to a gradual rise in temperature in the cowl 1 beyond the predetermined value. The slight heat expansion of the rod 8 would be enough to cause this drawback because of the very short differential travel of the switch 13.

However, this effect is neutralised because in prolonged use the bar 17 expands on heating and moves the switch 13 to the right in FIGS. 1 and 3. This displacement of the switch 13 is controlled by the expansion of strips 19, which takes place in an opposite direction with respect to the rod 17. The ratios of the length of strip 17 as well as of strips 19,, 20 and of their expansion coefficients to those of the rod 8 are such as to maintain the gap between the feeler 12 on the lever 10 and the portion of the switch 13 cooperating therewith constant, whereby stability in temperature of the cowl l is maintained under the said operational conditions.

It will be appreciated that details of construction of practical embodiments of this invention may be widely varied without departing from the effective scope of this invention.

What is claimed is:

1. In a heating arrangement for a dry copying machine of the type comprising a rotary cylinder, a substantially semicylindrical heating cowl of material having a high coefficient of thermal expansion spaced from the surface of the cylinder by a gap through which sheet material is passed in use of the machine, electrical heating means carried by said cowl, a switch controlling the heating means, said switch having a movable operating element which is actuated by thermal expansion of the cow] and a reaction rod connected at one end to said operating element, said reaction rod being of a material having a low coefficient of thermal expansion and extending parallel to the longitudinal axis of the cowl, and said reaction rod being fixed at its other end to said cowl, the improvement which consists a. a longitudinally extending rib on the centre part of the external surface of the cowl, said rib containing the electrical heating means;

b. two longitudinal flanges extending along the lateral sides of the rib and defining, together with the outer surface of the rib, a longitudinal channel;

0. a support carried by the two longitudinal flanges of the cowl at one end thereof;

means connecting one end of the reaction rod to said support;

e. a lever which co-operates with the movable switch operating element and on which the opposite end of said reaction rod acts;

f. means pivotally mounting between the longitudinal flanges at the end of the latter opposite that at which the support is carried;

g. at least one strip having a lower coefficient of thermal expansion than that of the cowl, attached to and extending longitudinally beyond said flanges adjacent the end of the cowl at which the support is carried;

h. a bar having high coefficient of thermal expansion extending within said channel and supporting the said switch at one end, and

i. means connecting said bar at its opposite end to said at least one strip.

2. The arrangement defined in claim 1, wherein the bar having a high coefficient of expansion is of alumi num and is supported by two said strips of iron which are attached to the external surfaces of the longitudinal flanges of the cowl.

=0 is =i l 

1. In a heating arrangement for a dry copying machine of the type comprising a rotary cylinder, a substantially semicylindrical heating cowl of material having a high coefficient of thermal expansion spaced from the surface of the cylinder by a gap through which sheet material is passed in use of the machine, electrical heating means carried by said cowl, a switch controlling the heating means, said switch having a movable operating element which is actuated by thermal expansion of the cowl and a reaction rod connected at one end to said operating element, said reaction rod being of a material having a low coefficient of thermal expansion and extending parallel to the longitudinal axis of the cowl, and said reaction rod being fixed at its other end to said cowl, the improvement which consists in: a. a longitudinally extending rib on the centre part of the external surface of the cowl, said rib containing the electrical heating means; b. two longitudinal flanges extending along the lateral sides of the rib and defining, together with the outer surface of the rib, a longitudinal channel; c. a support carried by the two longitudinal flanges of the cowl at one end thereof; d. means connecting one end of the reaction rod to said support; e. a lever which co-operates with the movable switch operating element and on which the opposite end of said reaction rod acts; f. means pivotally mounting between the longitudinal flanges at the end of the latter opposite that at which the support is carried; g. at least one strip having a lower coefficient of thermal expansion than that of the cowl, attached to and extending longitudinally beyond said flanges adjacent the end Of the cowl at which the support is carried; h. a bar having high coefficient of thermal expansion extending within said channel and supporting the said switch at one end, and i. means connecting said bar at its opposite end to said at least one strip.
 2. The arrangement defined in claim 1, wherein the bar having a high coefficient of expansion is of aluminum and is supported by two said strips of iron which are attached to the external surfaces of the longitudinal flanges of the cowl. 